Toner for electroradiography



United States Patent 20,840 V 2 Claims. Cl. 252-621) This invention relates to electroradiography, and in particular relates to a new and improved liquid dispersible toner material for the accurate rendition of continuous tone reproduction such as are required in electroradiography.

In the past various methods of toner formulation have been proposed, many of which have been of sufiiciently fine grain to be usable for continuous tone applications. However these toners have invariably been other than black in colour, and a serious limitation thus existed in which continuous tone toners, black in colour, were of coarser particle size and thus not satisfactory for the development of fine detail such as is required for instance in electroradiography. In addition most black toners are inherently of negative polarity and are only controlled to stable positive polarity by the addition of other agents which serve to further coarsen the image deposits. Also in the past binding agents added to the toner have tended to coarsen the image deposit with a resultant loss in definition.

I have now found that a black toner of such fineness suitable for continuous tone applications such as electroradiography and of positive polarity, suitable for dispersion in low cost hydrocarbon solvents can be formulated with adequate fixing properties utilizing an oleoresinous varnish which combines the properties of easy wetting of the pigment with suitable grinding and dispersing characteristi'cs, such varnish being so formulated that image deposits obtained from such toners display antisculf properties to a degree not hitherto possible with such fine grainedpositive acting toners. This varnish is compounded by the heating of hydrogenated rosin with linseed oil so that the resultant varnish has suitable dispersion characteristics in relatively low solvent power hydrocarbon solvents such as cyclohexane, n-heptane and the like.

The following examples will serve further to illustrate this invention.

Example 1 Grams Compound A 85 Microlith Black CT 20' Microlith Blue 4GT Microlith is the trademark of Ciba Ltd., for a range of resin dispersed pigments. Microlith Black CT is carbon ice black dispersed in hydrogenated rosin ester, and Microlith Blue 4GT is phthalocyanine blue dispersed in hydrogenated rosin ester.

These components were milled together in a bar mill, at a pressure of 200 psi, to assure uniform fine dispersion of the toner pigments in the varnish. The resultant toner base was then dispersed in cyclohexane in the proportion 1 gram toner paste to 5 grams cyclohexane, and

the thus formed cream diluted to working consistency with' 100 grams Shell Solvent X55, a substantially aliphatic solvent with a K.B. value of about 40. This toner was also dispersible in n-heptane, mineral turpentine, Shellsol T, a high boiling point aliphatic hydrocarbon solvent with a K.B. value of about 26, manufactured by the Shell Company, trichloromonofluoromethane, trichlorotrifluoroethane, and Solvesso 100, a substantially aromatic'hydrocarbon solvent of K.B. value about 93, manufactured by Esso-Atlantic. In each of these various carrier liquids the toner was of positive polarity, and the fineness of image deposit was suitable for continuous tone applications in all carrier liquids with a K.B. value greater than about 40.

Example 2 ,Grams Compound A of Example 1 Carbon Black SRF 35 Victoria Blue 5 This toner was milled and dispersed as in Example 1.

The resultant dispersion was somewhat finer than that of Example 1, and was maintained in carrier liquids with K.B. values above about 30.

This toner was milled and dispersed as in Examples 1 and 2 and the resultant dispersion was finer than that of either of the other two examples. It will be observed that the amount of toner used is about 30 to 40 parts by weight to about 85 parts by weight of the varnish obtained by heating the linseed oil and hydrogenated rosin at a temperature and for a time sufiicient to produce solution. The preferred weight ratio of rosin to oil is about 1:4, and the preferred weight ratio of varnish to carrier liquid is about 1:100.

It will be appreciated that in each instance the fineness of the obtainable image deposit was dependent to a degree on the particle size of the toner pigment selected, and that the varnish did not cause any coarsening of the dispersion due to incompatibility of such varnish with the dispersing medium. In addition adequate fixing properties were maintained without coarsening of the image deposit.

What I claim is:

1. In a method of preparing a substantially black developer of positive polarity for the development of electrostatic images: preparing a varnish consisting essentially of heating about one part by weight hydrogenated rosin in the presence of about four parts by weight of polymerized linseed oil having a viscosity of about 7.0-9.5 poises and at a temperature of about 235 F. for about one-half hour until solution is complete; adding to the varnish a toner consisting essentially of carbon black in a predominating amount and blue pigment in a minor amount, said toner being present in the proportion of about 30 to 40 parts by weight of toner to about 85 References Cited by the Examiner parts by weight of varnish, and milling to disperse the UNITED STATES PATENTS toner 1n the varnish; and subsequently dlspersmg the medium so formed in a carrier liquid in the proportion of 2,348,594 5/1944 Bernardl 10629 about one part by weight of medium to about 100 parts 5 2,907,674 10/1959 Metcalfe at v XR by weight of carrier liquid, the carrier liquid being a OTHER REFERENCES hydrocarbon solvent with a K.B. value between about 26 and 93 Chemical Abstracts, vol. 52, column 211571) 1959 2. A method according to claim 1 wherein the carrier liquid is selected from the group consisting of cyclohex- 10 JULIUS GREENWALD P'lmary Exammer' ane, n-heptane, and trichlorotrifiuoroethane. J. D. WELSH, Assistant Examiner. 

1. IN A METHOD OF PREPARING A SUBSTANTIALLY BLACK DEVELOPER OF POSITIVE POLARITY FOR THE DEVELOPMENT OF ELECTROSTATIC IMAGES: PREPARING A VARNISH CONSISTING ESSENTIALLY OF HEATING ABOUT ONE PART BY WEIGHT HYDROGENATED ROSIN IN THE PRESENCE OF ABOUT FOUR PARTS BY WEIGHT OF POLYMERIZED LINSEED OIL HAVING A VISCOSITY OF ABOUT 7.0-9.5 POISES AND AT A TEMPERATURE OF ABOUT 235*F. FOR ABOUT ONE-HALF HOUR UNTIL SOLUTION IS COMPLETE; ADDING TO THE VARNISH A TONER CONSISTING ESSENTIALLY OF CARBON BLACK IN A PREDOMINATING AMOUNT AND BLUE PIGMENT IN A MINOR AMOUNT, SAID TONER BEING PRESENT IN THE PROPORTION OF ABOUT 30 TO 40 PARTS BY WEIGHT OF TONER TO ABOUT 85 PARTS BY WEIGHT OF VARNISH, AND MILLING TO DISPERSE THE TONER IN THE VARNISH; AND SUBSEQUENTLY DISPERSING THE MEDIUM SO FORMED IN A CARRIER LIQUID IN THE PROPORTION OF ABOUT ONE PART BY WEIGHT OF MEDIUM TO ABOUT 100 PARTS BY WEIGHT OF CARRIER LIQUID, THE CARRIER LIQUID BEING A HYDROCARBON SOLVENT WITH A K.B. VALUE BETWEEN ABOUT 26 AND
 93. 